Apparatus for stage-wise nitration of toluene



APPARATUS FOR STAGE-WISE NITRATION F TOLUENE Original application Feb.25, 1957, Ser. No. 642,147. Divided and this application Feb. 19, 1959,Ser. No. 794,455

'16 Claims. (Cl. 23-266) This invention relates to novel tubularnitration procedures and apparatus for nitration of toluene. Moreparticularly, this invention relates to novel tubular nitrationprocedures and apparatus by which toluene is nitrated in two stages toform trinitrotoluene. In the first stage of nitration according to thisinvention, toluene is partially nitrated to an average nitrogen lcontentbetween about 14.5 and about 16.5 and in the second stage of nitrationpartially nitrated toluene having a nitrogen content between about 14.5%and about 16.5 is further nitrated to form trinitrotoluene.

It is well-known, of course, that toluene is a material which nitratesin stages corresponding generally to mononitrotoluene, dinitrotoluene,and finally trinitrotoluene, and numerous multistage nitration processeshave been proposed for the manufacture of trinitrotoluene. Insubstantially all of these prior art processes, the operation is reallya modified batch process in that high holdup vessel-type nitrators areemployed. Moreover, extensive circulation, recirculation, and arelatively long residence time of the reaction mixture in the nitratingzone `are characteristics of a majority of the previously proposedmethods, and such features are inherently undesirable because they favordegradative side reactions. Such degradative side reactions occur inprior art processes in all stages of the nitration of toluene totrinitrotoluene, particularly in the final stage.

It is a primary object of the present invention, therefore, to providenovel and unique tubular nitration procedures and apparatus whichovercome the above-noted characteristic faults of prior art methods.

A further object of the present invention is to provide an improvedtwo-stage nitration process and apparatus for manufacture oftrinitrotoluene from toluene.

Another object is to provide improved nitration procedures and apparatusin which there is a minimum amount of nitrated toluene product inprocess at any time.

Still other objects of this invention include: 4

Provision of improved nitration procedures which are much more rapid andin which there is a minimum of side reactions encountered in comparisonto prior art methods of nitration.

Provision of improved nitration procedures and apparatus which areunique in their simplicity in comparison to prior art methods.

Provision of improved nitration procedures and apparatus whereinpositive control of the process is easily and readily accomplished.

Provision .of improved nitration procedures and apparatus which requireonly simple, relatively inexpensive equipment and buildings incomparison to prior art methods. AOther objects will become apparentfrom the following description of the invention, the novel features andcombinations being set forth in the appended claims.

lGenerally described, these objectives and others are accomplished.bycontinuously feeding .a stream of re- 2,951,746l Patented i Sept. 6,1960 actant material selected from the group consisting of toluene andpartially nitrated toluene having an average nitrogen content betweenabout 14.5% and about 16.5% by weight and mixtures thereof through atubular path to a tubular reaction zone, simultaneously and continuouslyfeeding a stream of nitrating acid through a second tubular path to saidtubular reaction zone, impinging the separate streams of reactantmaterial and nitrating acid upon each other in Said tubular reactionzone to form a reaction mixture stream in the tubular reaction zone,continuously advancing said reaction mixture stream through said tubularreaction zone to f orrn a reaction product containing nitrated toluenehaving a higher nitrogen content than the originalk reactant material.

More particularly, the above objectives and others are accomplished inaccordance with this invention by (a) continuously feeding a stream oftoluene througha tubular path to a tubular reaction zone, (b)simultaneous.- ly and continuously feeding a stream of n itrating 4acidcontaining between about 60% and about 85% sulfuric acid, between about10% and about 30% nitric acid, and between about 3% and about 16% waterby weight on a contaminant free basis through a second tubular path tosaid tubular reaction zone, (c) impinging the separate streams oftoluene and nitrating acid upon each other to form a reaction mixturestream in the tubular reaction zone, (d) continuously advancing theresultant reaction mixture stream through the tubular reaction zonewhile regulating the temperature of said reaction mixture stream betweenabout 40 C. and about 140 C. until the toluene has been partiallynitrated to an av.- erage nitrogen content between about 14.5% and about16.5 by weight, and (e) continuously discharging `the reaction mixturestream into a separating zone and there separating spent nitrating acidjfrom partially nitrated toluene having an average nitrogen COIltentbetween about 14.5% and about 16.5% by weight. The above combination ofprocess steps (a) yto (e), ninclusive, constitutes the first stage ofnitration in accordance with this invention. The partially nitratedtoluene product obtained in the first stage of nitration is composedsubstantiallyV of dinitrotoluene, with relatively minor amounts ofmononitrotoluene and trinitrotoluene. Lt lis quite similar incomposition to the product heretofore known in lthe art as Bi-Oil,employed `as an explosive ingredient in various high explosive formulas,and has been found to be satisfactory equivalent to `Bi-Qil ,las Ia highexplosive ingredient. In accordancewith one embodiment of thisinvention, therefore, the partially nitrated toluene product which isseparated from spent nitrating acid in step (e) of the tirst stage ofnitration may then be puried by conventional methods and the purifiedproduct employed as an` equivalent to commercial Bi-Oil, as for example,an explosive ingredient in high explosive formulas.

However, -for trinitrotoluene manufacture, the partially nitrated-toluene product from step (e.) of the first stage of nitration is thensubjected to a second stage o f nitration by (f) continuously feeding astream of the separated partially nitrated toluene product from step (e)at a temperature above its melting point and under pressure through atubular path to a high temperature tubular reaction zone maintained at atemperature between about'90 C. and about 140 C., (g) simultaneously andcontinuously feeding a stream of trinitration acid under pressurethrough a second tubular path to said high temperature tubular reactionzone, (h) impinging the :separate streams of molten partially nitratedtoluene product and -trinitration acid Vupon each other under` pressureto form-a reaction-mixture -streamin the high temperature tubularLreaction zone, (if) continuously ad'-A vancing' the resultantV reactionmixture stream under pressure through the high temperature tubularreaction zone until substantially all of the partially nitrated tolueneproduct has been nitrated .to.trinitrotoluene, `(j) continuouslyadvancing the reaction mixture stream under pressure through a tubularcooling zone to cool said reaction mixture below about 100 C. andabovethe freezing point of said reaction mixture and (k) thereafterseparating trinitrotoluene from spent trinit'ratio'n acid, the pressurein step (1') being suicient to prevent any substantial vaporization ofnitric acid during the nitration reaction.'

The combinationof steps (f) to (k), inclusive, constitutes the secondstage of nitration, and may be practiced independentlyA for thecontinuous manufacture of trinitrotoluene from dinitrotoluene preparedby any method, or from commercial Bi'-Oil. The combination of steps (a)to (k), inclusive, constitutes a continuous two-stage process for themanufacture of trinitrotoluene from toluene.

In one `embodiment of the invention,'it has been found desirable in thefirst stage of nitration to (a.) continuously feedra stream of toluenethrough a dividedtubular path to a tubular reaction zone, (b)simultaneously and continuously feed a stream of nitrating acidcontaining between about 60% and about 85% sulfuric acid, between faboutand about 30% nitric acid, and between about 3% and about 16% water byweight on a contaminant free basis through a second tubular path to saidtubular reaction zone, (c) impinging the stream of nitrating acid andone branch of the divided stream of toluene upon each other to form areaction mixture stream in the ytubular reaction zone, and (d)thereafter injecting the remainder of the divided stream of toluene intothe reactionV mixture stream in the tubular reaction zone. Greatlyimproved control of the reaction in the iirst stage of nitration isachieved by dividing the toluene feed and injecting the divided streamat two or more points along the tubular reaction zone.. Y Anr alternatemethod for achieving improved control of the first-stage nitrationreaction embodies continuously recycling vpart of the reaction mixturestream, upon substantial completion of the first-stage nitrationreaction, through a tubular cooling zone and injecting the cooled streaminto. the main reaction mixture stream in the initial part of thetubular reaction zone. A.

It has also been found desirable in practicing the second stage-ofnitration to maintain lan initial part or portion of the hightemperature tubular reaction zone adjacent to'the converging feedstreams of molten partially Y 4 feed tubes converging and junctioningwith said first-stage tubular reactorY at one end thereof, said toluenefeed tube communicating with a toluene supply source and having meansassociated therewith for feeding a stream of toluene at predetermined owrate through said toluene feed tube to the first-stage tubular reactor,said first-stage nitrating acid feed tube communicating with afirst-stage nitrating acid supply source and having means associatedtherewith for feeding a stream of rst-stage nitrating acid atpredetermined flow rate through said first-stage nitrating acid feedtube to the first-stage tubular reactor,l

means associated with the first-stage tubular reactor'to control. andregulate the temperature of the first-stage reaction mixture thereinbetween about 40? C. and about 140 C., a first-stage separator disposedto receive the first-stage reaction mixture discharged from thefirst-stage tubular reactor, a heated storage vessel communicating Ywith the first-stage separator for receiving separated partiallynitrated toluene having an average nitrogen content between about 14.5%and about 16.5% by weight 'and maintaining said partially nitratedtoluene Vabove its melting point, an ielongated hightemperature'second-r stage tubular reactor having a communicatingpartially nitrated toluene feed tube and a communicating trinitrating`acid feed tube, `said feed tubes converging and junc-V tioning withsaid high temperature second-stage tubular reactor at the intakeendrthereof, said partially nitrated Y toluene feed tube communicatingwith the heated partially nitrated toluene storage vessel and havingmeans associated therewith for feeding a stream of molten partiallynitrated toluene under pressure at predetermined ow rate through saidpartially nitrated toluene feed tube to the high temperaturesecond-stage tubular reactor, said trinitrating acid feed tubecommunicating with a trinitrating acid supply source and having meansassociated therewith for feeding a stream of trinitrating ,acid underpres-l sure at a predetermined iiow rate through said trinitrating acidfeed tube to the high temperaturev second-stage Ytubular reactor,`meansassociated with the high temperature second-stage tubular Vreactorfor maintaining saidV reactor at a temperature between about 90 C. `andaboutv 140 C., an elongated cooling tube communicating at oneend thereofwith the 'discharge end of the high temperature second-stage tubularreactor, said cooling tube having means associated therewith formaintaining the temperature of said cooling tube below about 100 C. andabove the freezing point of the' second-stage reaction mix-1 ture, meansassociated with the high temperature second nitrated toluene andtrinitration acid at a temperature v between about 90 C. andabout 120lC., and the remainder of the high temperature tubular reaction zone at ahigher temperature than said initial part and between about 110 C. andabout 140 C. This promotes better control of the second-stagenitration.Y Preferably, but not necessarily, the reaction mixturestreams in both the firstand second-stage nit-rations are advancedthrough their respective tubular reaction zones at flow ratescorresponding to a Reynolds number of at least about 2100 and sufcientto maintain turbulent flow in the reaction mixtures.

In a preferred embodiment of the invention, spent trinitration acid,after separation from trinitrotoluene, is recovered and adjusted incomposition-byV adding aqueous nitric acid thereto to form a nitratingacid containing between about 60% and about 85% sulfuric acid, betweenabout 10% and about 30% `nitric acid, and between about 3% and about 16%water by weight on a contaminant free basis and then recycling theyadjusted acid composition asnitrating acid to the first-stagenitration.

Y Improved4 apparatus for practicing nitration of toluene in two stagesin accordance with this invention oomprises in combination an elongatedfirst-stage tubular reactor having a communicating toluene feed tube anda communicating first-stage nitrating .acid ffdstube, saidstage tubularreactor and cooling .tube for maintaining the second-stage reactionmixture therein under sufficient pressure to prevent any substantialvaporization ofnitric acid from said reaction mixture, and asecond-stage separator disposed to receive the second-stage Ireactionmixture after cooling thereof for separating trinitro-y toluene fromspent trinitrating acid. Y

When it is desired vto practice the invention Ias a continuous cyclicprocess,` the apparatus set forth hereinabove is augmented with aspentftrinitrating acid storage vessel communicating with thesecond-stage separator, and aqueous nitric acid supply source, and anacid mix tank; said spent trinitrating acid storage vessel and saidaqueous nitric acid supplyV source each communicating with said `acidmix tank, and said acid mix tank in turn communi-j cating with thefirst-stage tubular reactor.

Improved apparatus for practicing the first stage 'of nitration inaccordance with this invention comprises in combination an elongatedfirst-stage tubular reactor having a communicating toluene feed tube anda communicating first-stage nitrating acid feed tube, said feed tubesconvergingA and junctioning with said first-stage tubularre# actor atone end thereof, said toluene feed tube communicatingwith a toluenesupply source andhaving means.

n associated therewith for feedinga streamy of toluene-at predeterminedrilowrate'through said toluene feed tube to feed tube communicating witha first-stage nitrating acid supply source and having means associatedtherewith for feeding a stream of rst-stage nitrating acid atpredetermined flow rate through said first-stage nitrating acid feedtube to the first-stage tubular reactor, means associated with thefirst-stage tubular reactor to control and regulate the temperature ofthe first-stage reaction mixture therein between about 40 C. and about140 lC., and a first-stage separator disposed to receive the first-stagereaction mix- -ture discharged from the first-stage tubular reactor forseparating partialy nitrated toluene having an average nitrogen contentbetween about 14.5 and about 16.5% by weight from spent first-stagenitrating acid.

In another embodiment of first-stage nitration apparatus, the toluenefeed tube is divided into at least two branches, one branch of whichconverges with the first-stage nitrating acid feed tube and junctionswith the first-stage tubular reactor at the intake end thereof, and atleast one branch of which junctions with said tubular reactor at adistance from said intake end. Preferably, the partially nitratedtoluene storage vessel is associated with heating means to maintain saidpartially nitrated toluene above its melting point.

In still another embodiment of first-stage nitration apparatus, there isprovided an elongated cooling tube, the intake end of which junctionsand communicates with the first-stage tubular reactor near the dischargeend thereof and the discharge end of which junctions and communicateswith said first-stage tubular reactor adjacent the intake end thereof tocool and recycle part of the first-stage reaction mixture.

Improved apparatus for practicing second-stage nitration in accordancewith this invention comprises in combination an elongated second-stagetubular reactor having a communicating partially nitrated toluene feedtube and a communicating tri-nitrating acid feed tube, Said feed tubesconverging and junctioning with said second-stage tubular reactor at theintake end thereof, said partially nitrated toluene feed tubecommunicating with a heated storage vessel containing molten partiallynitrated toluene having an average nitrogen content between about 14.5%and about 16.5% by weight, said partially nitrated toluene feed tubehaving means associated therewith for feeding a stream of said moltenpartially nitrated toluene under pressure at predetermined flow ratethrough said partially nitrated toluene feed tube to the hightemperature secondstage tubular reactor, said trinitrating acid feedtube communicating with a trinitrating acid supply source and havingmeans associated therewith for feeding a stream of -trinitrating acidunder pressure at a predetermined flow rate through said trinitratingacid feed tube to the high temperature second-stage tubular reactor,means associated with the high temperature second-stage tubular reactorfor maintaining said reactor at a temperature between about 90 C. andabout 140 iC., an elongated cooling tube communicating at one endthereof with the discharge end of tie high temperature second-stagetubular reactor, said cooling tube having means associated therewith formaintaining the temperature of said cooling tube below about 100 C. andabove the freezing point of the second-stage reaction mixture, meansassociated with the high temperature second-stage tubular reactor andcooling tube for maintaining the second-stage reaction mixture thereinunder sufficient pressure to prevent any substantial vaporization ofnitric acid from said reaction mixture, and a second-stage separatordisposed to receive the second-stage reaction mixture after suitablecooling thereof for separating trinitrotoluene from spent trinitratingacid.

In one preferred embodiment of the invention, an initial part of thehigh temperature second-stage tubular reactor adjacent the convergingfeed tubes is associated with heating means for maintaining said initialpart at a temperature between about 90 C. and about 120 C., and theremainder of said second-stage tubular reactor is associated with otherheating means for maintaining the temperature '6 of said remainder at ahigher temperature than said initial part and between about C. and about140 C.

A preferred embodiment of the invention has been chosen for purposes ofillustration and description and is shown inthe accompanying drawingforming a part of the specification, in which reference symbols refer tolike parts whenever they occur and in which gauges and otherconventional auxiliary equipment have been omitted for simplicity.

Fig. 1 is a diagrammatic drawing illustrating the features of thisinvention.

Fig. 2 is a diagrammatic drawing illustrating divided toluene feed inaccordance with one embodiment of this invention.

Fig. 3 is a diagrammatic, fragmentary, cross-sectional view illustratingone embodiment for the junction of tubular feed lines with tubularreactors employed in` both lirstand second-stage nitrations, asillustrated at A- andY B in Fig. 1.

Fig. 4 is a diagrammatic drawing illustrating cooling and recycle ofpart of the first-stage reaction mixture in accordance with anotherembodiment of this invention.

Referring to the drawing, toluene from supply tank 11 via line 12 is fedthrough pump 13 in predetermined pro-l portions via valved line 14 totubular reactor 15. Valve 16 in line 14 is a quick opening by-pass valvewhich is normally closed. However, upon shutdown for anyy reason, thisValve can be instantly opened to shut off the supply of toluene to thetubular reactor and return the toluene via line 17 to toluene supplytank 11. Simultaneously, the first-stage nitrating acid, containingbetween about 60% and about 85% sulfuric acid, between about 10% andabout 30% nitric acid, and between about 3% and about 16% Water byweight on a contaminant free basis, from supply tank 18 is fed via line19 through pump 21 in predetermined proportions via line 22 to tubularreactor 15.

It will be seen from the drawing that tubular feed lines 14 and 2-2converge and junction with tubular reactor 15 at one end thereof, and inthe embodiment lillustrated in Fig. l the two tubular feed lines and thetubular reactor form a simple T-tube section, as illustrated at A inFig. 1, free of moving parts, as illustrated in Fig. 3. T-he separatestreams of toluene and first-stage nitrating acid thus converge andimpinge upon each other to form a reaction mixture stream in tubularreactor 15 at the point where the two tubular feed lines junction withtubular reactor 15.

The reaction mixture stream is then advanced through tubular reactor 15lat a ow rate corresponding toa Reynolds number of at least about 500,and preferably at a flow rate corresponding to a Reynolds number of atleast about 2100 and suicient to maintain turbulent flow in the reactionmixture stream, whereupon toluene reacts with the first-stage nitratingacid to form a partially nitrated toluene having `an average nitrogencontent be` tween about 14.5% and about 16.5% by weight. The reactionmixture is then discharged fro-m tubular reactor 15 at 23 into separator24 where partially nitrated toluene is separated from spent first-stagenitrating acid which is drawn 0E via line 25. Since spent first-stagenitrating acid contains some dissolved partially nitrated toluene havinga nitrogen content between about 14.5% and I[about 16.5% by weight,suchspent acid may be subjected to extraction with toluene to recover thepartially nitrated toluene therefrom, and the toluene extract thusobtained can then be cycled to the first-stage nitration reaction tonitrate the toluene therein to va product containing 14.5% to 16.5%nitrogen by weight. 26 having inlet 26a and outlet 26h is a conventionalcooling bath, as for example, ya circulating water bath, surrounding atleast part of tubular reactor 15, to--control and regulate thetemperature of the reactionmixture in tubular reactor 15 at atemperature between" about 40 C. and about 140C. l I- In .a preferredpractice of 'this invention, it has been 7 found desirable to injectWater into the first-stage reaction mixture upon substantial completionof the iirst-stage nitration reaction and prior to separation of thepartially nitrated toluene from spent first-stage nitrating acid.Dilution of the reaction mixture with water enhances recovery of thepartially nitrated toluene by reducing its solubility in spent acid. Aconvenient means for accomplishing such water dilution is illustrated inFig. 1 by which water via line 28 is injected at 27 into the reactionmixture in tubular reactor 15. An alternate arrangement for waterinjection is illustrated in Fig. 4.

In one embodiment of the invention, illustrated diagrammatically in Fig.2, it has been found desirable to introduce the toluene feed at apluralityof points along tubular reactor 15 in order to achieveimpro-ved control of the nitration reaction. Accordingly, with referenceto Fig. 2, the supply stream of toluene via line 14 is divided and onebranch thereof is fed to tubular reactor 15 via line 29, and theremainder of the toluene is fed to tubular reactor 15 via line 31 and isinjected into the reaction mixture in tubular reactor 15 at one or morepoints along tubular reactor 15, as at 32 and yat 33.

In another embodiment of the invention, illustrated diagrammatically inFig. 4, part of the first-stage reaction mixture, upon substantialcompletion of the iirststage nitration reaction but prior to Waterinjection into thereaction mixture, is recycled via proportioning valve71, line 72, cooling tube 73,-and line 74 and the cooled mixture isinjected into the main reaction mixture stream in tubular reactor 15 at76. 75 having inlet 75a and outlet V75b is a conventional cooling bathsurrounding cooling tube 73. l

The partially nitrated toluene having an average nitrogen contentbetween about 14.5% and about 16.5%,

produced in the above iirst-stage nitration of toluene inV accordancewith this invention, upon separation from spent first-stage nitratingacid in separating zone 24 may be Iwithdrawn from the process via line34 for conventional washing and purification treatment, and may then beemployed as an explosive ingredient in high explosive formulas or inother applications Which utilize substantially dinitrotoluene or Bi-Oil.

However, when it is desired Vto prepare trinitrotoluene in accordancewith this invention, the partially nitrated toluene from the first-stagenitration is subjected to a second stage of nitration. Accordingly,partially nitrated toluene from separating zone 24, with or withoutsubsequent washing and puriiication treatment, is conveyed by a line 35to storage tank 36 which is preferably heated to a temperature above themelting point of the partially nitrated toluene by means of heating coil77 having inlet 77a `and outlet 77 b, or by equivalent means.

Partially nitrated toluene having an average nitrogen content betweenabout 14.5% and yabout 16.5% from heated storage tank 36 is then fed viajacketed line 37, pump 38 and jacketed line 39 in predeterminedproportions under pressure and at a temperature above its melting pointto high temperature tubular reactor 41. Simultaneously, anhydnoustrinitration -acid from supply tank 42 via line 43 is fed through pump44 and jacketed line 45 in predetermined proportions under pressure andat an elevated temperature to high temperature tubular reactor 41. Y

It will be seen from the drawing that jacketed feed lines 39 and 45 andtubular reactor 41 form a simple T-tube section, as illustrated at B inFig. l, free of moving parts, as illustrated in Fig. 3. The separatestreams of molten partially nitrated toluene and anhydrous trinitrationacid thus converge yand impinge upon each other to form preferably aturbulent reaction mixture stream in high temperature tubular reactor41. The reaction mixture stream is then continuously advanced underpressure through high temperature tubular reactor 41 at ya flow ratecorresponding to a Reynolds number otgatgleast aboutjOO, .preferably ataflow .rate

8 corresponding to a Reynolds number of at least about 2100 and sucientto maintain turbulent ow in the reaction mixture, whereup'on partiallynitrated toluene reacts with anhydrous trinitration acid to formtrinitrotoluene. 46 having inlet 46a and outlet 4612 and 47 having inletA'47a and outlet 47b are'conventional heat` control means which may beintegral or separated, `as de-q sired, surrounding high temperaturetubular reactor 41 to maintain said reactor at a temperature betweenabout` C. and about 140 C.

The reaction mixture containing trinitrotoluene in spent trinitrationacid is then continuously advanced under pressure through cooling tube48 maintained at a temperature below about C. and above the freezingpoint of the second-stage reaction mixture. 49'having inlet 49a andoutlet 49b is a conventional heat exchange means surrounding coolingtube 48.

In one embodiment ofV this invention, it Vhas been found desirable toinject nitric Vacid of about 98% HNO3 content into thereaction mixtureuponsubstantial completion of the second-stage nitration reaction andprior to separation of trinitrotoluene from spent trinitrating acid.Such nitric acid injection into the reaction mixture rgreately enhancesrecovery of trinitrotoluene by reducing its solubility in spenttrinitrating acid. A convenient means for such nitric acid introductionis illustrated in Fig. 1 by which 98% vnitric acid via line 51 isinjected at 52 into the reaction mixture in cooling tube 48.

The reaction mixture is then continuously discharge from cooling tubeV48 into separator 54 through pressure tube 53 having a smaller insidediameter than cooling tube 48. 53a is a'steam jacket surroundingpressure tube Y53. Trinitrotoluene is separated from spent trinitratingacid in separating zone 54 and is withdrawn from the process via line 55for conventional washing and purification treatment. Separated spenttrinitrating acid from separating zone 54 is transported via line 56 tostorage tank 57 from which it is conveyed via line 58, pump 59 and line61 to'mixed acid storage tank 62. Aqueous nitric acidV from supply tank'63 is also conveyed to mixed acid storage tank 62 via line 64, pump 65and line 66. Spent trinitrating acid and aqueous nitric acid are mixedin predetermined proportions in mixed acid storage tank 62 to adjust thecomposition of the spent trinitrating acid to contain between about 60%and about 85% sulfuric acid, between about 10% and about 30% nitricacid, and be` tween about 3% and about 16% water by weight on acontaminant free basis, and the adjusted acid composition is thenrecycled as first-stage nitrating acid via line 67, pump 68 and line 69to supply tank 18.

In a preferred embodiment of second-stage nitration in accordance withthis invention, it has been found desirable to maintain an initial partof high temperature tubular reactor 41 adjacent the intake end whichjunctions with jacketed feed lines '39 and 45 at a lower temperaturethan the remainder of high temperature tubular reactor 41, andpreferably at a temperature between about 90 C. and about C., theremainder of high temperature tubular reactor 41'being maintainedbetween about 110 C. and about C. This improves control of the reaction.Accordingly, heat control means 46 and heat control means 47 areindependent of each other in this embodiment of this invention asindicated by line X in Fig. 1. An isothermal boiling water bath has beenfound to be convenient and practical as heat control means'46, whereasheat control means 47 can conveniently be an isothermal boilingchlorobenzene bath (132 Itwill be understood, however, that theinvention is not limited in this respect, since obviously other heatcontrol means within the skill of the art can be employed. Asanalternative arrangement, heat control means 46 and 47 can betemperature gradient from about .90 C., at the intake end 9 of reactor41 adjacent to B to about 140 C. at the discharge end adjacent tocooling tube 48.

Successful practice of this invention in both first-'stage andsecond-stage nitration processes requires means for the positive feedand proportioning of the respective reactant feed streams of tolueneandVrst-stage nitrating acid for rst-stage nitration and of partiallynitrated toluene and trinitrating acid for second-stage nitration, andany means which will accomplish such positive feed and proportioning isequivalent for the purposes of this invention. For example, meteringpumps, gear pumps, centrifugal pumps, pressure exerted by hydraulichead, pressure exerted by gas under constant pressure, pressureaccumulators, and the like, in combination with metering devices whennecessary or desirable, or any combination of such means can beemployed.

In the embodiment illustrated in the drawing, it will be seen thatreactant feed lines 14 and 22 junction with tubular reactor 15 to form asimple T-tube Section as at A. Similarly, reactant feed lines 39 and 45junction with tubular reactor `41 to also form a simple T-tube sectionas at B. However, the invention is not limited to employment of T-tubejunctions at A and B since the only requirement is that the respectivereactant feed lines in both first-stage and second-stage nitrationapparatus converge and junction with the respective tubular reactor ineach stage so that the respective reactant streams of toluene andfirst-stage nitrating acid in first-stage nitration and partiallynitrated toluene and anhydrous trinitrating acid in second-stagenitration will impinge upon each other. Accordingly, any geometricconfiguration of the respective reactant feed lines with theirrespective tubular reactor which will accomplish the purposes of thisinvention can be employed, as desired.

It is an important characteristic of this invention that there are nomoving parts in either the first-stage or second-stage tubular reactors.Turbulent flow is relied upon for eiectuating intimate dispersion oftoluene in :firststage nitrating acid in first-stage nitration, and foreffectuating intimate dispersion of partially nitrated toluene andanhydrous trinitrating acid in second-stage nitration, and formaintaining the respective reaction mixtures in emulsified form in theirrespective tubular reactors. The rates of flow of the reactant feedstreams of toluene and first-stage nitrating acid in first-stagenitration and of partially nitrated toluene and anhydrous trinitratingacid' in second-stage nitration are regulated so that upon impingementupon each other, they preferably form turbulent reaction mixtures in therespective tubular reactors. No further mixing is required. It is afurther characteristic in both first-stage nitration and in second-stagenitration according to the present invention that both the first-stageand second-stage reaction mixtures positively and continuously advancethrough their respective tubular reactors.

The first-stage nitration reaction is highly exothermic, commencingimmediately upon mixing the toluene with the first-stage nitrating acidand is very rapid, being substantially complete within a matter ofseconds or less under the preferred conditions of the invention, andseldom, if ever, requiring any longer than 60 seconds. Firststagenitrations may be made at temperatures as -low as 40 C. and as high as140 C. Degradative secondary reactions assume undesirable proportions inrelation to the desired nitration reaction at temperatures above about140 C., and such temperatures should, therefore, be avoided. It has beenfound that the first-stage nitration reaction rate is greatlyaccelerated with increasing temperature. Accordingly, therefore, thefirst-stage nitration reaction should preferably be conducted at as higha ternperature as possible consistent with the avoidance of undesirabledegradative side reactions. In the preferred practice of this invention,it has been found desirable to regulate the temperature of the rst-stagereaction mixture within the range betweenabout 60 C. and about 105 C.

toluene product.

In. the embodiment illustrated in Fig. 1, a-cooling bath 26 is employedas a convenient means for control-l ling and regulating the temperatureof the first-stage reaction mixture stream within the operativetemperature range. However, the invention is not limited lin this-respect, for other means may be employed to regulate and control thetemperature of the first-stagey reaction mixture. For example,multi-toluene injection, as illustrated in Fig. 2, can be employedeither aloneA or in conjunction with other temperature regulative means,or part of the reaction mixture can be recycled througha cooling coiland the cooled mixture injected into the main reaction mixture, asillustrated in Fig. 4. lf desired, either or both of the reactantstreams of toluene and first-stage nitrating acid may be chilled priorto introduction to tubular reactor 15. Presently preferred means forternperature control of the first-stage reaction mixture are illustratedin Figs. 2 and 4. Whereas several alternative means have been disclosedfor regulating the temperature ofthe first-stage reaction mixturebetween about: 40: C. and about 140 C., the invention is by no meanslimited thereby, for various other expedients for accomplishing suchtemperature regulation are within the skill of the art. The importantfeature is regulation and control of the temperature of the first-stagereaction mixture within the limits set forth, and any means orcombination of means which will accomplish such regulation and controlare equivalent and within the scope ofk this invention.

It will be apparent from the foregoing description that residence timeof the first-stage reaction mixture in the first-stage tubular reactionzone, in accordance with preferred practice of this invention, is ofvery brief duration, amounting usually to only a few seconds, but shouldbe sufiicient to accomplish substantially complete nitration of tolueneto an average nitrogen content betweenabout 14.5% and about 16.5%. Thelength of the first-stage tubularreaction Zone to accomplish thepurposes ofthis invention can readily be calculated from desiredtemperature and iiow rate information, and can readily be checked bysimple analysis of the partially nitrated The inside diameter of thefirst-stage tubular reactor will be governed `largely bythe projectedproduction throughput capacity desired fromthe apparatus, keeping inmind the Reynolds Number requirements of the invention. Y

The second-stage nitration reaction, in which partially` nitratedtoluene having an average nitrogen content between about 14.5 and about16.5% is nitrated to trinitrotoluene, is comewhat slower-thanvfirst-stage nitration, but is nevertheless quite rapid in comparison toprior art methods,being substantially complete within a matter of fromabout 2 to 6l minutes under the preferred-` conditions of the invention,and seldom, if ever, requiring longer than about 12 to 15 minutes. tionin accordance with this invention must be carried out in a heatedtubular reactor at a temperature above about 907 C. to proceed at allsatisfactorily, and reaction rate increases with increasing temperature.However, above about l40 C., degradative Side reactions assumeundesirable proportions in relation to the desired nitration reaction,and such temperatures should be avoided. The operative temperature rangefor secondstage nitration in accordance with this invention, therefore,lies between a lower temperature of about C., below which thetrinitration reaction does not proceedv satisfactorily, and an uppertemperature of about C., above which degradative side reactions assumeundesirable proportions. Since reaction rate is acceleratedwithincreasing temperature, the second-stage, nitrationreaction ispreferably conducted at as high a temperature as possible, consistentwith the avoidance of yundesirable degradative side reactions. `In thepreferred practice of this invention, it has been found `desirable tomaintainanlinitiallpart of the high temperaturesecond- Second-stagenitraanis '1,7118 Y.

11 Y. l stage tubular reactor adjacent to B at'a lower temper-` aturethan the remainderof the high temperature second. stage tubular reactor,since, as pointed out hereinbefore, this practice enhancesrcontrol ofthe second-Stage reaction.

Residence time of the second-stage reaction Vmixture in the hightemperature second-stage tubular reaction` zone should be as short aspossible in accordance with preferred practice of this inventionconsistent with substantial completion of the nitration of partiallynitrated toluene to trinitrotoluene in order to reduce as far aspossible degradative side reactions. v

Generally, in accordance with preferred practice of this invention,residence time in the initial lower temperature portion of the hightemperature second-stage tubular re-V action zone will be on the orderof 1-2 minutes, and residence time in the remainder ofthe hightemperature second-stage tubular reaction zone maintained at a highertemperature will be on the order of 2-4 minutes. The length of thesecond-stage tubular reactor to accomplish the purpose of this inventioncan be readily calculatedV from desired temperature andrlow rateinformation, and can be easily checked by simple analysis of theeffluent product. The inside diameter of -the second-stage tubularreactor will be governed largely by the projectedl production throughputcapacity desired for the apparatus, keeping in mind the Reynolds Numberrequirements of the invention. Y,

Upon completion of the second-stage nitration reaction, the second-stagereaction mixture containing trinitrotoluene in spent trinitrating acidshould be cooled to a temperature below about 100 C. in'order to inhibitdegradative side reactionsfrom taking place to reduce yields oftrinitrotoluene, and above the freezing point of the second-stagereaction mixture to prevent plugging the `tubular cooling coil. A hotWater bath at and about 16.5% from freezing. Accordingly, the tern-`perature of .the partially` nitrated toluene is maintained at atemperatureabove its melting point by transporting it inliquid form froma heated supply tank through jacketed lines sucheas 37' and 39 in Fig. 1heated with hot Water, steam, circulatedhot .air, and the like with orVWithout insulation. Preferably, but not necessarily, the feed stream oftrinitrating acid may be preheated to an elevated temperature at leastas high as the temperature of the molten partially nitrated toluene feedstream before introducing it to the second-stage tubular reactor at B.This may be conveniently accomplishedY bypassing the trinitrating acidthrough a jacketed line such as 45 in Fig. 1` heated with hot water,steam, circulatedl hot air, and the like with or without insulation.This Vprevents freezing-out of the partially nitrated toluene inthesecond-stage tubular reactor adjacent to B upon impinging the two feedstreams together, and also favors more rapid initiation of secondstagenitration.`

According to the present invention, both the first-stage reactionmixture'and the second-stage reaction mixture are each advanced throughtheir respective tubular reaction zones at a flow rate corresponding toa Reynolds number of at least about 500, and preferably at a ow ratecorresponding to a Reynolds number of at least about 2100 vandsufficient to maintain turbulent flow in the respective reactionmixtures. 'Reynolds number, according to Badger and'McCabe, Elements ofChemical Engineering,

about 80 C. surrounding tubular cooler 48v has been found to be aconvenient means for cooling the secondstage reaction mixture Vto thedegree necessary for the purposes of this invention. However, theinvention is not limited to employment of a hot water bath at about 80C., since numerous other means within the skillof the art can beemployed to cool the second-stage reaction mixture to the extentindicated hereinaboveV as necessary for the purposes of this invention.Y

It is ya characteristic feature in the preferred practice of thisinvention to maintain the second-stage reaction mixture at a pressuresuiciently high to prevent any substantial evaporation of nitric acidfrom the second-stage reaction mixture during the second-stage nitration'and subsequent cooling of the second-stage reaction mixture; This isconveniently accomplished bypassing the sec` ond-stage reaction mixturefrom cooling coil 48 into and through a section of tubing 53 of smallerinside diameter than that of tubular cooler 48 before discharge of thesecond-stage 4reaction mixture into second-stage separator 54. Tubing 53may, if desire, form an extension of restricted inside diameter ofcooling tube 48. In the preferred practice of this invention, tubing 53`of restricted inside diameter must be maintained at a tem- -peratureabove the freezing point of the second-stage re-j action mixture. Thisis conveniently accomplished by enclosing tubing 53 within a steamjacket. This invention is not limited to the use of restricted insidediameter pressure tube, however, since Vany means V,within the skill ofthe art for maintaining the second-stage reaction mixture at suicientpressure to substantially prevent vaporization of nitric acid therefromduring the sec-l ond-stage nitration reaction is operative inaccordancel with this invention. For example, apressure controller inthe line between cooling tube 48 and second-stage separator 54 may beemployed if,V desired.

In practicing second-stage nitration, precaution must be exercised toprevent the partially nitrated toluene having an average nitrogencontent between labout 14.5 %vk 1936 Ed., page 28, is readily calculatedfrom the following engineering formula: Y

Reynolds number -Il-p in terms metric, units:

D=inside diameter kof tube in cm.

u=linear velocity `of liquid stream in cm./ sec. p=density of liquid'ingJ/cc.'Y f

p.=viscosity of liquid inl poises AtRe-ynolds'number above about 2100,the flow of a liquid in smooth tubes-y generally assumes a turbulentcharacter'.` For' the purposes of this invention, completely turbulentow is'not necessary,`since successfulA nitrationsin both -rst-stagenitratrion and in second-stage nitra-` tion have been made atReynoldsnumbers-ofapproximatej ly 500. However, to keep the reaction time to aminimum land the; efficiency, of heat transfer atY a maximum, itisdesirable thattlie Reynolds number be at least about 2100.First-stagenitr'ating acid -in accordance with this inventioncontain'sbetween about 60% 'and about 85% sulfuric acid, between aboutV10%V and about 30% nitric acid, and between.about3% and about 16% waterby weight, with or withoutsmall percentages of trinitrotoluene andnitration contaminants from second-stage nitration, depending, Vuponwhether therrst-stage nitratingV acid is formulated withV fresh nitricand sulfuric acids or is formulated by adjusting thlecomposition. ofspent trinitrating acid from second-stage nitration with aqueous nitricacid. Between about 4 `parts and about 200parts of first-stagenitratingacid per' partof toluene by weight can be employed inpracticing this invention, and preferably between about 5 parts andabout 25 parts by` weight per part of toluene. Y j Trinitrating aidemployed in. second-stage nitration to nitrate partially knitratedtoluene having an average nitrogen content between about 14.5% andabout16.5 to trinitrotoluene Ycontains between about 60% and about sulfuricacid, between about ,5%. and about 40%V nitric acid,and between about 0%and about 35% free sulfur' trioxide, and w'illbe Vemployed to the extentof between about ,2 parts andabout 2 5 parts per part of partiallynitrated toluene bygweight, and preferably between about 2.5 partsand-aboutv 5l pr s per part of partiallynitrated tluenefbyiweig'ht. e Y

The followingexa'mplesr'set forth somespecificembodijacket.

vs olidiiies.

that these examples, while illustrative, are not to be con- Astrued as alimitation of the invention.

Example 1 k This example illustrates an embodiment of first-stagenitration in which partially nitrated toluene having an average nitrogencontent between about 14.5% and about 16.5% was prepared by nitratingtoluene with first-stage nitrating acid containing 82.2% sulfuric acid,14.1% nitric acid, and 3.7% water in a tubular reactor.

The tubular reactor for this example consisted of three coiled sectionsof 3pg-inch inside diameter stainless steel tubing joined together endto end and totaling 100 feet in length. The first coil section, 40 feetlong, adjacent the intake end at which the toluene and nitrating acidfeed lines joined the tubular reactor, was insulated. The next coilsection, 40 feet long, was jacketed and was maintained at W-105 C. bypassing steam through the The nal coil section, feet long, adjacent thedischarge end of the tubular reactor was immersed in a warm water bathmaintained at 50 C. The tubular reactor was joined at the intake endthereof by means of a T-tube section, as at A in Fig. l, with thenitrating acid and toluene feed lines, each of iis-inch inside diameterstainless steel tubing.

A constant nitrogen gas pressure of 40 p.s.i. was impressed fon thenitrating acid supply in a blow case to feed the nitrating acid to thetubular reaction zone. An electrically driven metering pump (a MiltonRoy Constametric, Milton Roy Co., 1300 East Mermaid Lane, Philadelphia18, Pennsylvania) in the toluene feed line fed the toluene to thetubular reaction zone. The reactant feed streams of toluene andnitrating acid were impinged upon each other to form a turbulentreaction mixture stream in the tubular reactor, and toluene reacted withthe nitrating acid in the tubular reactor to form partially nitratedtoluene having an average nitrogen content between about 14.5% and about16.5 by weight. The reactionv mixture stream was discharged from thetubular reactor into anice and water drowning bath from .which thepartially nitrated toluene product was separated and recovered. Therecovered partially nitrated toluene was then washed three times withhot water, dried, and the product analyzed. This product was found to besatisfactory as an explosive ingredient in high explosive compositions.It was also found that the recovered partially nitrated toluene productcan be readily nitrated to trinitrotoluene with anhydrous trinitratingacid in a second stage ofnitration.

Pertinent data relative tothe nitration and the recovered productfollow:

Toluene feed rate gJmin-- 49.6 Nitrating acid feed rate g./min 1148 Feedratio of nitrating acid to toluene (by weight) 23.1 Ratio of nitric acidto toluene (by weight) 3.25 Residence time of reaction mixture intubular reactor min 0.9 Maximum recorded temperature in reaction mixtureC 114 VNitrogen content of recovered partially nitrated toluene (byweight) percent 15.7 Setting point of recovered partially nitratedtoluene C 51 Setting point is the tem erature at which the productExample 2 27% nitric acid, and 5.3% water in a tubular reactor.

The tubular reactor for this example consisted of a 20- foot`coiledfsection of G-inch inside diameter stainless pumpwas employed inboth the nitrating acid feed line and in the toluene feed line to feedthe respective reactants to the tubular reactor. The metering pumpsemployed were Milton Roy Constametric pumps (see 'Example l formanufacturer and address thereof). The reactant feed streams of tolueneand nitrating acid were impinged upon each other to form a turbulentreaction mixture stream in the tubular reactor, and toluene reacted withthe nitrating acid in the tubular reactor to form partially nitratedtoluene having an average nitrogen content between about 14,5% and about16.5 The reaction mixture stream was discharged from the tubular reactorinto an ice and water drowning bath, from which the partially nitratedtoluene product was separated and recovered. The recovered partiallynitrated toluene was then washed three times with hot water, dried, andthe product analyzed. This product was found to be satisfactory as anexplosive ingredient in high explosive compositions. It was also foundthat the recovered partially nitrated toluene product can be readilynitrated to trinitrotoluene with anhydrous trinitrating acid in a secondstage of nitration.

Pertinent data relative to the nitration and the reof first-stagenitration in which in each embodiment partially nitrated toluene havingan average nitrogen content between about 14.5% and about 16.5 wasprepared bynitrating toluene with a first-stage nitrating acidcontaining 67.7% sulfuric acid, 27% nitric acid, and 5.3% water inatubular reactor.

Thetubular reactor and nitrating acid feed line for these threeembodiments were substantially the same as set forth in Example 2.However, in each of the three embodiments illustrated in this example,the main toluene feed stream from a E'ym-inch inside diameter feed linewas divided into two approximately equal branches and was injected intothe tubular reactor at two points on the tubular reactor as illustratedin Fig. 2. One branch of the toluene feed stream was fed into thetubular reactor at the T-tube junction of the tubular reactor with thenitrating acid feed line, where this branch of the toluene feed streamand the nitrating acid feed stream impinged upon each other to form aturbulent reaction mixture in the tubular reactor. The remainder of thetoluene feed stream was injected into the reaction mixture in thetubular reactor at a point on the tubular reactor 9 feet from theinitial T-tube junction illustrated at A in Fig. 2. Milton RoyConstametric pumps in both the main toluene feed line and in thenitrating acid feed line were employed to feed the respective reactantsto the tubular reactor, as in Example 2. In each embodiment toluenereacted with nitrating acid in the tubular reactor to form partiallynitrated toluene having an average nitrogen content between about 14.5%and about 16.5 The partially nitrated toluene product in each embodimentwas separated, washed, and recovered substantially asset forth Run A RunB Run C Toluene feed rate (g./min.) 64. 8 60. 6 64. 8 Nitrating acidfeed rate (gJmin.) 752. 2 552.1 489.1 Feed. ratio of nitrating acid totoluene (by weight 11.6 9.1 7. Ratio of nitric acid to toluene (byweight). 3. 1A 2. 4 2 Residence time of reaction mixture in tubularreactor (min.) 0.1 0. 1 0. 1

Maximum recorded temperature in reaction mixture C.) 103 98 97 Nitrogencontent of recovered partially nitrated toluene (percent by weight) 15.2 15.1 14. 8 Setting point of recovered partially nitrated toluene C.)55. 5 55. 5 55 Example 4 This example illustrates an embodiment ofsecond-stage nitration in which trinitrotoluene was prepared bynitrating partially nitrated toluene having a nitrogen content of 16.1%with anhydrous trinitrating acid containing 70.7% sulfuric acid, 16%nitric acid, and 13.3% free sulfur trioxide in a high temperaturetubular reactor under presv sure. l

The high temperature tubular reactor employed in this embodimentconsisted of two coiled sections of 1i-inch inside diameter stainlesssteel tubing joined together end to end and totaling 160 feet innlength.The first coil section, 40 feet long, adjacent the intake and atwhichthe partially nitrated toluene and anhydrous nitrating acid feedlines joined the high temperature tubular'reactor, was immersed in aboiling water bath (100 C.). The second coil section, 120 feet long, wasimmersed in a boiling chlorobenzene bath (132 C). The discharge end ofthe second coil section of thehigh temperature tubular reactor wasjoined to a cooling coil 40` feet long of i-inch inside diameterstainless steel tubing immersed in a circulating 80 C. .water bath. Thedischarge end of the 40-foot cooling coil in turn 'was joined to a7-foot length of steam jacketed stainlesssteel pressure tubing havingan' inside diameter of 1A@ inch, which was discharged into an ice andwater drowning bath. The high temperature tubular reactor was joined atthe intake end thereof by means of a T-tube section, as at B in Fig. 1,with the anhydrous tri-nitrating acid and partially nitrated toluenefeed lines, eachof 1i-inch inside diameter steam jacketed (100 C.)stainless steel tubing.

A constant nitrogen gas pressure of 150 p.s.i.g. was impressed on theanhydrous trinitrating acid supply in a blow case to feed the nitratingacid under pressure continuously to the high temperature tubularreactor. A Milton Roy Constametric pump in the partially nitratedtoluene feed line fed the molten partially nitrated toluene underpressure continuously to the high temperature tubular reactor. Thereactant feed streams of Aanhydrous trinitrating acid and moltenpartially nitrated toluene were impinged upon each other to form aturbulent reaction mixture stream under pressure in the high temperaturetubular reactor, and the resultant reaction mixture stream wascontinuously advanced through. the 40-foot isothermal coil at 100 C.,thence through the v1Z0-foot isothermal coil at 132 C., during whichpas- :sage through the two coiled sections of the high temperaturetubular reactor, the partially nitrated toluene reacted with theanhydrous trinitrating acid in the high temperature tubular reactor toform trinitrotoluene. The reaction mixture stream was then continuouslyadvanced through the 4 0-fopt cooling coil at 80 C., thence through the7-foot length of ysteam jacketedpressure tubing, and was continuouslydischarged therefrom into an ice and water drowning bath, from whichtrinitrotoluene was separated iand recovered. The recoveredtrinitrotoluene was then washed three times with boiling water, cooled,dried, and the product was analyzed.

Pertinent data relative to the Anitration and recovered product follow:

Partially nitrated toluene feed'rate g./min 101.2 Anhydrous trinitratingacid feed rate g./min 247.4 Feed ratio of anhydrous trinitrating acid topartially nitrated toluene (by weight) 2.44 Ratio of'nitric acid toYpartially nitrated toluene (by weight) 0.39 Residence time of reactionmixture in high temperature tubular reactor min -4.3 Nitrogen content ofrecovered trinitrotoluene (by weight) percent-- 18 Setting point ofrecovered trinitrotoluene C 67 Example 5 This example illustrates twoadditional embodiments of second-stage nitration in which `in eachembodiment trinitrotoluene was prepared by nitrating a partiallynitrated toluene with :an anhydroustrinitrating acid in a hightemperature tubular reactorunder pressure. The anhydrous trinitratingacid and the partially nitrated toluene employed in both embodimentswere the same as employedin Example 4. The apparatus and procedure werealso substantially the same as set forth in Example 4 except that a20-foot coiled length of steam iiacketed stainless steel pressure tubinghaving an inside diameter of 1/16 inch was employed in the twoembodiments of this example instead of the 7-footlength employed inExample 4. v

Pertinent data relative to the tw embodiments of this example follow:

Partially nitrated toluene feed rate (g./min. 43. 9 74. 3 Anhydroustrinitrating acid f eed rate (g../min.). 270 V219 Feed ratio ofanhydrous trinitrating acid to partially Y i.

nitrated toluene (by weight) L 6. 15 2. 95v Ratio of nitric acid topartially nitrated toluene (by weight) 0. 98 0. 47 Residence time ofreaction mixturein high temperature f tubular reactor (min.) 5 5.2Nitrogen content of recovered trin rotoluene (percent r by weight) 18. 518. 5 Setting point of recovered trinitrotoluene C.) 77 74 Example 6nitrating acid employed in both embodiments was the same as employed inExample 4. The partially nitrated toluene employed in embodimenttia ofthis example vhad an average nitrogen content of V161.1%, whereas thepartially nitrated toluene employed in embodiment 6b of this example hadan average n'trogen content of 15.2%: The apparatus and procedureemployed in the embodiments of this example were the same lasset forthinExample 5 with the following exceptions: (l) a Milton Roy-Constametricpump was employed inthe embodimentsof this example to continuously feedthe anhydroustrinitratmg acid to the high temperature tubular reactorinstead' of a Ynitrogen gas pressured blow case as Example 5; '(2) the1Z0-foot coil section of the high temperature tubular reactor for theembodiments of this example wasY immersed in a constant boiling mixtureof water 'andY chlorobenzene boiling at 118 C. instead of in a boilingchloroben-zene bath boiling at 132 C as inl-Example 51; (iiD-'thereaction mixture stream Vin the embodiments of this example wasdischarged from the steam jacketed 1,s-inch inside diameter pressuretubing into a steam jacketed separatory funnel instead of into an iceand Water drowning bath as in Example 5, and the trinitrotoluene wascontinuously separated in molten form from spent trinitrating acid,Washed three times with boiling Water, chilled, dried, and analyzed. Thespent trinitrating acid was drawn off and recovered.

Pertinent data relative to the two embodiments of this example follow:

Partially nitrated toluene feed rato (g./min.) 26. 6 46. 2 Anhydroustrinitrating acid feed rate (glmin.) 77. 4 220. 5 Feed ratio ofanhydrous trinitrating acid to partially nitrating toluene (by Weight)2. 91 4. 78 Ratio of nitric acid to partilly nitrated toluene (byweight) 0. 47 0. 77 Residence time otreaetion mixture in hightemperature tubular reactor (min.) 12. 5 5. 4 Nitrogen content ofrecovered trinitrotoluene (percent by weight 1s. 4 1s. 5 Setting pointof recovered trinitrotoluene C.) 72 70 Example 7 This exampleillustrates an embodiment of the invention in which toluene was nitratedby a continuous cyclic process in two stages to form trinitrotoluene. Inthe first stage of nitration of this embodiment, toluene Wascontinuously nitrated to a partially nitrated toluene having an averagenitrogen content of 15.2% with a firststage nitrating acid containing67.7% sulfuric acid, 27% nitric acid, and 5.3% water by Weight in atubular reactor. The product from the first stage of nitration was thenfurther continuously nitrated with an anhydrous trinitrating acidcontaining 70.7% sulfuric acid, 16% nitric acid, and 13.3% free sulfurtrioxide to trinitrotoluene in a second stage of nitration in a hightemperature tubular reactor under pressure, and spent trinitrating acidwas adjusted in composition with an aqueous nitric acid to formfirst-stage nitrating acid which was recycled to the first-stagenitration reaction.

For the first stage of nitration the tubular reactor consisted of acoiled section of 3/16-inch inside diameter stainless steel tubing 20feet in length immersed in a circulating tap water bath, and a dividedtoluene feed line was employed. One branch of the toluene feed line andthe first-stage nitrating acid feed line joined the tubular reactor atthe intake end thereof in a T-tube section, and the remaining branch ofthe toluene feed line joined the tubular reactor 9 feet from the T-tubejunction, as illustrated in Fig. 2. The first-stage nitrating acid andthe toluene feed lines were 3Alg-inch inside diameter stainless steeltubing, and Milton Roy Constametric pumps were employed in both thenitrating acid and toluene feed lines to meter the reactants to thetubular reactor. Water from line 28 Was injected into the reactionmixture at 27 following substantial completion of the first-stagenitration reaction but before separation of the partially nitratedproduct from spent first-stage nitrating acid, as illustrated in Fig. l.The reaction mixture from the first-stage tubular reactor was dischargedinto a jacketed separatory funnel with Water at about 60 C. circulatingthrough the jacket. Partially nitrated toluene Was continuouslyseparated from first-stage spent nitrating acid in the heated separatoryfunnel and was piped in molten state to a heated storage tank, fromwhich it was fed in predetermined proportions in molten state through asteam jacketed line to the high temperature tubular reactor employed insecondstage nitration.

For the second stage of nitration the high temperature tubular reactorconsisted of two coiled sections of :Vsinch inside diameter stainlesssteel tubing joined together end to end and totaling 160 feet in length.The first coil section, 40 feet long, adjacent the intake end at Whichthe partially nitrated toluene and anhydrous trinitrating acid feedlines joined the high temperature tubular reactor, was immersed in aboiling Water bath (100 C.). The second coil section, 120 feet long, wasimmersed in a boiling chlorobenzene bath (132 C.). The discharge end ofthe second coil section of the high temperature tubular reactor wasjoined to a cooling coil, 40 feet long, of 1A-inch inside diameterstainless steel tubing immersed in a circulating C. Water bath. Thedischarge end of the l0-foot cooling coil in turn was joined to a20-foot coiled length of steam jacketed stainless steel pressure tubinghaving an inside diameter of 1A; inch. The high temperature tubularreactor was joined at the intake end thereof by means of a T-tubesection, as at B in Fig. 1, with anhydrous trinitrating acid andpartially nitrated toluene feed lines, each of 3/s-inch inside diametersteam jacketed stainless steel tubing. Milton Roy Constametric pumpswere employed in both the anhydrous trinitrating acid feed line and inthe partially nitrated toluene feed line to feed the respectivereactants to the high temperature tubular reactor. The second-stagereaction mixture was discharged from the steam jacketed 1x-inch insidediameter pressure tubing into a steam jacketed separatory funnel Wheretrinitrotoluene was continuously separated in molten form from spenttrinitrating acid, Washed three times with boiling Water, chilled,dried, and recovered for use. Spent trinitrating acid from theseparatory funnel Was piped to a spent trinitrating acid storage tank.Part of the spent trinitrating acid from the storage tankwas piped to amixing tank where it Was adjusted in composition by adding aqueousnitric acid thereto to reconstitute firststage nitrating acid which wasthen recycled to the firststage nitration.

In carrying out this example, first-stage nitrating acid from a supplytank was continuously pumped to the tubular reactor at the rate of 752.2g./min. Simultaneously, toluene from a supply tank was continuouslypumped to the tubular reactor at a total rate of 64.8 g./min. in adivided stream. The feed ratio of firststage nitrating acid to tolueneby Weight was 11.6. The ratio of nitric acid to toluene by weight was3.2. One branch of the toluene feed stream Was fed into the firststagetubular reactor at the T-tube junction of the firststage tubular reactorwith the first-stage nitrating acid feed line, where this branch of thetoluene feed stream and the first-stage nitrating acid feed streamimpinged upon each other to form a turbulent reaction mixture stream inthe first-stage tubular reactor. The remainder of the divided toluenefeed stream was continuously injected into the reaction mixture streamin the first-stage tubular reactor at a point on the tubular reactor 9feet from the initial T-tube junction. The reaction mixture stream wascontinuously advanced through the tubular reactor, during whichadvancement the toluene reacted with the first-stage nitrating acid inthe first-stage tubular reactor to form a partially nitrated toluenehaving an average nitrogen content of 15.2% by weight, and the maximumtemperature in the reaction mixture during nitration was 103 C. Uponsubstantial completion of the nitration reaction, but before dischargingthe reaction mixture from the first-stage tubular reactor, water fromline 28 was injected into the reaction mixture lat 27 at the rate of28.1 g./min. Residence time of the reaction mixture in the first-stagetubular reactor Was about 8 seconds.

The first-stage reaction mixture was then continuously discharged at therate of 845.1 g./min. into a jacketed separatory funnel having hot waterat about 70 C. circulating through the jacket. Partially nitratedtoluene having an average nitrogen content of 15.2% and a setting pointof 55.5 C.was continuously separated from spent first-stage nitratingacid in the heated separatory funnel and was conveyed in molten state atthe rate of 125.6 g./min. to a storage tank heated to about 70 C.Separated spent first-stage nitrating acid from the 19 heated separatoryfunnel was withdrawn from' the process. l

Partially nitrated toluene from the heated storage tank was continuouslypumped at the rate of 125.6 g./min. under pressure in molten statethrough a steam jacketed line to the second-stage high temperaturetubular reactor. Simultaneously and continuously, anhydrous trinitratingacid was pumped at the rate of 600 g./min. under pressure through asecond steam jacketed line to the secondstage high temperature tubularreaction. The feedratio of anhydrous trinitrating acid to partiallynitratedtoluene was 4.78, and the ratio of nitric acid to partiallynitrated toluene was 0.77. The two reactantv feed streams impinged uponeach other at the point where the two reactant feed lines joined thehigh temperature tubular reactor at B in Fig. 1 to form a turbulentsecond-stage reaction mixture stream in the high temperature tubularreactor, and the reaction mixture stream then was continuously advancedunder pressure through the 40-foot coil immersed in boiling water,thence through the 120- foot coil immersed in boiling chlorobenzene,thence through the 40-foot cooling coil immersed in the circulatingwater bath at 80 C., and finally through the 20- foot section of steamjacketed pressure tubing, and was continuously discharged at the rate of725.6 g./min. from the pressure tubing into a steam jacketed separatoryfunnel. Residence time of the second-Stage reaction mixture in the hightemperature tubular reactor consisting of the 100 C. isothermal 40-footcoil and the 132 C. isothermal 120-foot coil was approximately 5minutes, during which partially nitrated toluene yreacted withtrinitrating acid to form trinitrotoluene.

Molten trinitrotoluene was continuously separated from spenttrinitrating acid in the steam jacketed separatory funnel and was drawnoff, washed three times with boiling water, crystallized, dried, andwithdrawn from the process. The yield of trinitrotoluene wasapproximately 141 g./rnin., having a nitrogen content .of 18.5% byweight and a setting point of 70 C.`

Separated spent nitrating acid from the separatory funnel containing83.4% sulfuric acid, 9.3% nitric acid, and 7.3% sulfur trioxide, wasconveyed at the rate of 569.1 g./min. to a storage vessel. 552 g./min.of 'this spent trinitrating acid was pumped from the storage vessel to amixing tank where it was mixed with 200.2.g./min. of aqueous nitricacidV containing 75.6% nitric acid and 24.4% water to form 752.2 g./min.of first-stage nitrat- 20 advantagesof the present invention reside inthe attainment of the objectives as set forth hereinabove. Thisapplication is a division of our application for United States LettersPatent Serial No.` 642,147, rtiled February 25, 1957.v c What we claimand desire to protect by Letters 'Patent 1. Apparatus for manufacture oftrinitrotoluene from toluene in two stages of nitration comprising incombination an elongated first-stage tubular reactor having a toluenefeed tube and a first-stage nitrating acid feed tube, said feed tubesconverging and junctioning with said first-stage tubular reactor at theintake end thereof, said toluene feed tube communicating with a toluenestorage vessel, said first-stage nitrating acid feed tube communicatingwith arst-stage nitrating acid storage vessel; separaterfirst-stagefeeding means associated with both the toluenefeed tube and thefirst-stage nitrating acid feed tube for force feeding the reactants tothe firststage tubular reactor at predetermined ow rates; a firsttemperature regulating means associated with the firststage tubularreactor for maintaining temperature thereof between about 40 C. andabout 140 C.; a first-stage separator disposed to receive first-stagereaction mixture discharged from the lfirst-stage tubular reactor forseparation of partially nitrated toluene from spent first-stagenitrating acid; a heated storage vessel communicating with thefirst-stage separator for receiving separated partially nitrated tolueneand maintaining the same above its melting point; an elongatedsecond-stage tubular reactor having a partially nitrated toluene feedtube and a second-stage nitrating acid feed tube, said feed tubes ingacid containing 67.7% sulfuric acid, 27% nitric acid,

and 5.3% Water which was recycled to the first-stage nitration;

It is apparent from the foregoing description that this inventionprovides novel and improved apparatus and procedures for the nitrationof toluene'in stages having many advantages over prior art methods andapparatus for this purpose. The present invention provides apparatus andprocedures which are unique in their simplicity, economy, chemicalefficiency, and time-saving characteristics in relation to prior artmethods and apparatus. Moreover, the present invention providesilexibility in separation of spent nitrating acid from the -nitratedtoluene product in both iirst and second stages of nitration, since suchseparation can be accomplished either by gravity separation or bycentrifugal separation. Furthermore, the present invention providesimproved ease of temperature control, provides positive metering ofreactants, the opportunity for multi-injection of toluene in rst-stagenitration, the opportunity for-cooling and recycling part of thefirst-stage reaction mixture, the opportunity to conduct second-stagenitration under pressure to prevent vaporization, and the opportunity toinject water or nitric acid at suitable points into the reactionmixtures to decrease solubility of the desired product in the reactionmixtures, none of which are provided .by prior art methods andapparatus.

Other important converging and junctioning with said second-stagetubular reactor at the intake end thereof, said partially nitratedtoluene feed tube communicating with the heated storage vessel, saidsecond-stage nitrating acid feed tube communicating with an anhydroustrinitrating acid storage vessel; separate second-stage feeding meansassociated with both the partially nitrated toluene feed tube and thesecond-stage nitrating acid feed tube for forcefeeding the reactants tothe second-stage tubular reactor at predetermined flow rates; a secondtemperatureV regulating means associated with the second-stage tubularreactor for maintaining temperature thereof between about C. and about140 C.; an elongated cooling tube communicating at the intake endthereof with the discharge end of the second-stage tubular reactor; athird temperature regulatingl means associatedV with the cooling tubefor maintaining temperature thereof below about CQ and above thefreezing point of secondstage reaction mixture; flow-restrictive meansassociated with' the cooling tube for exerting back pressure onsecond-stage reaction mixture in the second-stage tubular reactor andcooling tube; and a second-stage separator disposed to receive cooledsecond-stage reaction mixture discharged from the cooling tube forseparating trinitrotoluene from spent second-stage nitrating acid.

2. Apparatus in accordance With claim 1 which is augmented with a spentsecond stage nitrating acid storage vessel communicating with thesecond-stage separator, a fresh nitric acid storage vessel, and an acidmix tank, said spent second-stage nitrating -acid storage vessel andsaid fresh nitric acid storage vessel each communicating with said acidmix tank, and said acid mix tank in turn communicating with thefirst-stage tubular reactor, Y

3. Apparatus in accordance with claim 1 in which the feedingmeansyassociated with the feed tubes for force feeding toluene andfirst-stage nitrating acid in predetermined proportions to thefirst-stage tubular reactor are il mi tion means disposed to injectwater into the reaction mixture in the first-stage tubular reactor nearthe discharge end thereof.

6. Apparatus in accordance with claim l in which the toluene feed tubeis divided into at least two branches, one branch of which convergeswith the first-stage nitrating acid feed tube and junctions with thefirst-stage tubular reactor at the intake end thereof, and at least onebranch of which junctions with said first-stage tubular reactor at adistance from said intake end.

7. Apparatus in accordance with claim 1 in which there is provided anelongated cooling tube, the intake end of said cooling tube junctioningand communicating with the rst stage tubular reactor adjacent thedischarge end thereof and lthe discharge end of said cooling tubejunctioning and communicating with said first-stage tubular reactoradjacent the intake end of said. first-stage tubular reactor to cool andrecycle part of the first-stage reaction mixture.

8. Apparatus in accordance with claim l in which the first-stageseparator is a centrifuge.

9. Apparatus in accordance with claim 1 in which the rst-stage separatoris a gravity separation vessel.

l0. In apparatus for the stage-wise nitration of toluene thesubcombination comprising an elongated second-stage tubular reactorhaving la partially nitrated toluene feed tube and a second-stagenitrating acid feed tube, said feed tubes converging and junctioningwith said second-stage tubular reactor at the intake end thereof, saidpartially nitrated toluene feed tube communicating with a heated storagevessel containing molten partially nitrated toluene, said second-stagenitrating acid feed tube communicating with an anhydrous trinitratingacid storage vessel; separate second-stage feeding means associated withboth the partially nitrated .toluene feed tube and fthe second-stagenitrating acid feed tube for force-feeding the reactants to thesecond-stage tubular reactor at predetermined iiow rates; temperatureregulating means associated with the second-stage tubular reactor formaintaining temperature thereof between about 90 C. and about 140 C.; anelongated cooling tube communicating at the intake end thereof with thedischarge end of the second-stage tubular reactor; other temperatureregulating means associated with the cooling tube for maintainingtemperature thereof below about 100 C. and above the freezing point ofsecond-stage reaction mixture; flow-restrictive means associated withthe cooling tube for exerting back pressure on second-stage reactionmixture in the second-stage tubular reactor and cooling tube; and asecond-stage separator disposed to receive cooled second-stage reactionmixture discharged from the cooling tube for separating trinitrotoluenefrom spent second-stage nitrating acid.

11. Apparatus in `accordance with claim 10 in which saidflow-restrictive means is an elongated tube having a smaller internalcross-sectional area than the internal cross-sectional area of saidcooling tube, the intake end of said tube of smaller internalcross-sectional area communicating with the discharge end of saidcooling tube and the discharge end of said tube of smaller internalcross-sectional Iarea communicating with the second-stage separator.

12. Apparatus in `accordance with claim 10 in which an initial part ofthe second-stage tubular reactor adjacent the intake end thereof hastemperature-regulating means associated therewith for maintaining saidinitial part at a temperature between about C. and about 120 C., and theremainder of said second-stage tubular reactor has separatetemperature-regulating means associated therewith for maintaining saidremainder at a higher temperature than said initial part between aboutC. and about 140 C.

13. Apparatus in accordance with claim 10 in which the second-stagefeeding means associated with the partially nitrated toluene feed tubeand with the second-stage nitrating acid feed tube are metering pumps.

14. Apparatus in 'accordance with ciaim 10 having injection meansdisposed to inject concentrated nitric acid into the reaction mixture inthe cooling tube.

15. Apparatus in accordance with claim 10 in which the second-stageseparator is a centrifuge.

16. Apparatus in accordance with claim 10 in which the second-stageseparator is la gravity separation vessel.

References Cited in the le of this patent UNITED STATES PATENTS 1,4 14,762 Townsend May 2, 1922 2,332,527 Pyzel Oct. 26 ,1943 2,418,241 StengelApr. 1, 1947 2,717,903 Ruth Sept. 13, 1955

1. APPARATUS FOR MANUFACTURE OF TRINITROTOLUENE FROM TOLUENE IN TWOSTAGES OF NITRATION COMPRISING IN COMBINATION AN ELONGATED FIRST-STAGETUBULAR REACTOR HAVING A TOLUENE FEED TUBE AND A FIRST-STAGE NITRATINGACID FEED TUBE, SAID FEED TUBES CONVERGING AND JUNCTIONING WITH SAIDFIRST-STAGE TUBULAR REACTOR AT THE INTAKE END THEREOF, SAID TOLUENE FEEDTUBE COMMUNICATING WITH A TOLUENE STORAGE VESSEL, SAID FIRST-STAGENITRATING ACID FEED TUBE COMMUNICATING WITH A FIRST-STAGE NITRATING ACIDSTORAGE VESSEL, SEPARATE FIRST-STAGE FEEDING MEANS ASSOCIATED WITH BOTHTHE TOLUENE FEED TUBE AND THE FIRST-STAGE NITRATING ACID FEED TUBE FORFORCE FEEDING THE REACTANTS TO THE FIRSTSTAGE TUBULAR REACTOR ATPREDETERMINED FLOW RATES, A FIRST TEMPERATURE REGULATING MEANSASSOCIATED WITH THE FIRSTSTAGE TUBULAR REACTOR FOR MAINTAININGTEMPERATURE THEREOF BETWEEN ABOUT 40*C. AND ABOUT 140*C., A FIRST-STAGESEPARATOR DISPOSED TO RECEIVE FIRST-STAGE REACTION MIXTURE DISCHARGEDFROM THE FIRST-STAGE TUBULAR REACTOR FOR SEPARATION OF PARTIALLYNITRATED TOLUENE FROM SPENT FIRST-STAGE NITRATING ACID, A HEATED STORAGEVESSEL COMMUNICATING WITH THE FIRST-STAGE SEPARATOR FOR RECEIVINGSEPARATED PARTIALLY NITRATED TOLUENE AND MAINTAINING THE SAME ABOVE ITSMELTING POINT, AN ELONGATED SECOND-STAGE TUBULAR REACTOR HAVING APARTIALLY NITRATED TOLUENE FEED TUBE AND A SECOND-STAGE NITRATING ACIDFEED TUBE, SAID FEED TUBES CONVERGING AND JUNCTIONING WITH SAIDSECOND-STAGE TUBULAR REACTOR AT THE INTAKE END THEREOF, SAID PARTIALLYNITRATED TOLUENE FEED TUBE COMMUNICATING WITH THE HEATED STORAGE VESSEL,SAID SECOND-STAGE NITRATING ACID FEED TUBE